One of the uses of an accelerometer is as a crash sensor for deploying a supplemental inflatable restraint device in an automotive vehicle in the event of a crash. While electromechanical type crash sensors have the most extensive commercial use at this time, it is contemplated that electronic accelerometers will enjoy increasing usage in the future as crash sensors.
One form of electronic accelerometer is a cantilever beam that has one end supported on a mount and a proof mass at the other. Such a beam can be micromachined from silicon, and one or more strain gauges disposed on its surface at a desired sensing situs. These one or more strain gauges are connected in an electric circuit to provide a signal indicative of acceleration-induced strain in the beam.
While a cantilever beam type accelerometer has the advantage of being more sensitive than certain other types of accelerometers to on-axis accelerations intended to be detected, it may also be prone to indiscriminately pick-up certain cross-axis accelerations as well, and the latter characteristic is typically deemed to be an undesirable attribute for an automotive crash sensor.
A simple beam type accelerometer that is supported at both ends and contains the proof mass in the middle is less sensitive to cross-axis accelerations, but has the disadvantages of being less sensitive to on-axis accelerations for a given beam length.
The present invention relates to a new and unique cantilever beam type accelerometer which has both greater on-axis sensitivity and lower cross-axis sensitivity. It has the further advantage of occupying a space whose dimension that runs along the length of the beam is less than that in the case of the known cantilever beam for a given level of on-axis sensitivity, and consequently the inventive accelerometer may offer certain fabrication and packaging advantages, such as occupying less space within an enclosure and providing improved batch yield because more may be produced from a given wafer size.
These features and advantages of the invention, and others as well, may be perceived by one's reading of the following detailed description which presents a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention. The following drawings form a part of the disclosure.